A liquid hydrogen carrier re-liquefaction system for recovering expansion work and its application

Abstract

The present invention provides a re-liquefaction system for a liquid hydrogen carrier ship that recovers expansion work and its application, comprising: a precooling unit, a hydrogen liquefaction unit, and a circulation unit; the precooling unit includes a first heat exchanger; the hydrogen liquefaction unit includes a second heat exchanger, a gas-liquid separator, and a subcooler; the gas-liquid separator and the subcooler form first and second return flow streams; the circulation unit includes at least one compressor unit and several expanders, which use gas-bearing expanders, and the gas source is hydrogen, provided by the compressor unit; each expander includes a compression end, which uses the expansion work of the expander to pressurize the gas; after the first return flow stream flows through the compression end of the expander from the second heat exchanger, it leads to the compressor unit and forms a circulating hydrogen gas flow stream. The present invention uses hydrogen expansion cooling to provide cold energy for hydrogen, and then uses gaseous hydrogen to recover the shaft work generated during the expansion process to compress the gaseous hydrogen. While recovering the compression work, it also reduces the usage and volume of the compressors in the system, and can reduce the compression energy consumption by 5% - 10%.

Description

[0001] This application is a divisional application.

[0002] The original application number was 202310848549.5, the application date was July 12, 2023, and the title was: A re-liquefaction system for a liquid hydrogen transport ship that recovers expansion work. Technical Field

[0003] The present invention belongs to the field of liquid hydrogen transportation, and particularly relates to a re-liquefaction system for a liquid hydrogen transport ship that recovers expansion work and its application. Background Art

[0004] The chemical energy of hydrogen is the energy generated by the reaction of hydrogen and oxygen. It does not depend on fossil fuels and mainly exists in the form of chemical compounds. It is a secondary energy source with rich sources, green and low-carbon, and wide applications. It is an important part of the future national energy system, which can help large-scale consumption of renewable energy, achieve large-scale peak shaving of the power grid and cross-seasonal and cross-regional energy storage, and accelerate the low-carbonization of industries, buildings, transportation and other fields.

[0005] At present, the main hydrogen storage methods are high-pressure gaseous storage and cryogenic liquid storage. High-pressure gaseous storage is the most common and direct hydrogen storage method, but the hydrogen storage capacity of this method is small, and it requires thick pressure-resistant storage tanks, so the transportation cost is very high. The cryogenic liquid storage technology is not yet mature. For a long time, many researchers have carried out a large number of theoretical and experimental studies on improving the liquefaction efficiency of hydrogen and reducing the liquefaction cost.

[0006] On a liquid hydrogen transport ship, since liquid hydrogen itself is extremely easy to evaporate, it is also necessary to supplement liquid hydrogen through hydrogen liquefaction technology. Since the main problems existing in current hydrogen liquefaction technology are still low liquefaction efficiency, large investment and high energy consumption. Therefore, improving the liquefaction efficiency and energy utilization efficiency is an urgent problem to be solved.

[0007] Hydrogen liquefaction generally includes an expansion step. At present, in the hydrogen liquefaction system, there are very few systems involving the recovery of expansion work. Moreover, most expanders use oil bearings, and when recovering expansion work, it will pollute the reverse-flow hydrogen. If there is too much oil in the reverse-flow hydrogen, the oil may solidify in the circulating hydrogen, resulting in blockage of the heat exchanger channels. If the oil needs to be removed, it will increase the operating cost of the system, which is not economical. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides a re-liquefaction system for a liquid hydrogen transport ship that recovers expansion work, so as to reduce the energy consumption in the hydrogen liquefaction process, improve the hydrogen liquefaction efficiency, and eliminate the pollution to hydrogen when recovering expansion work.

[0009] The present invention provides a re-liquefaction system for a liquid hydrogen transport ship that recovers expansion work, including: a precooling unit, a hydrogen liquefaction unit, and a circulation unit;

[0010] The pre-cooling unit includes a first heat exchanger for pre-cooling the feed hydrogen stream.

[0011] The hydrogen liquefaction unit includes a second heat exchanger, a gas-liquid separator, and a sub-cooler; the feed hydrogen stream leaves the pre-cooling unit, forms a gas-liquid two-phase after passing through the second heat exchanger, and reaches the gas-liquid separator, where the gas phase is denoted as the first reflux stream and returns to the second heat exchanger as a cold stream; while the liquid phase enters the sub-cooler and is cooled to 18K ± 5K, and then is split into a product stream and a second reflux stream; the product stream leads to a product collection container; the second reflux stream is throttled and depressurized and then returns to the sub-cooler and the second heat exchanger as a cold stream in sequence.

[0012] The circulation unit includes at least one compressor unit and several expanders; each expander includes a compression end that uses the expansion work of the expander to pressurize the gas; the expander is a gas-bearing expander; the bearing gas is hydrogen, which is provided by splitting a stream of hydrogen from the compressor unit or the compression end of the expander; before entering the bearing, the bearing gas is first depressurized to 0.6 - 0.8 MPa through a pressure reducing valve; the expander includes a first expander and a second expander, and the number of the first and second expanders is 0 - 4; after the first reflux stream passes through the compression end of the first expander from the second heat exchanger, and after the second reflux stream passes through the compression end of the second expander from the second heat exchanger, both lead to the compressor unit and merge, and the merged stream is denoted as the circulating hydrogen stream.

[0013] The circulating hydrogen stream is pre-cooled by the first heat exchanger and then split into an expansion stream and a make-up stream. After the make-up stream passes through the second heat exchanger, it reaches the gas-liquid separator.

[0014] After the expansion stream passes through the second heat exchanger and the expansion end of the expander to reduce the temperature and pressure, it flows back to the second heat exchanger and the first heat exchanger as a cold stream in sequence, and finally returns to the compressor unit and is incorporated into the circulating hydrogen stream.

[0015] The hydrogen liquefaction unit is also provided with a first J-T valve, a second J-T valve, and a third J-T valve for throttling and depressurizing; after the feed hydrogen stream passes through the second heat exchanger, it also passes through the first J-T valve to reduce the temperature and pressure and form a gas-liquid two-phase; after the make-up stream passes through the second heat exchanger, it also passes through the second J-T valve to reduce the temperature and pressure and form a gas-liquid two-phase; after the second reflux stream passes through the third J-T valve to reduce the temperature and pressure, it returns to the sub-cooler and the second heat exchanger as a cold stream in sequence.

[0016] A normal-to-parahydrogen catalyst is provided in the feed hydrogen channel of the second heat exchanger for continuous normal-to-parahydrogen conversion of the feed hydrogen.

[0017] The system includes a control device. Temperature sensors, pressure sensors, and flow sensors are respectively provided in the first heat exchanger, the second heat exchanger, and the ortho-para hydrogen converter, and are connected to the control device.

[0018] Preferably, the ortho-para hydrogen catalyst is selected from metal catalysts or magnetic catalysts, and the metal catalyst is one of iron, platinum, nickel, and palladium.

[0019] The present invention also discloses the application of this system on land, which is used for the hydrogen liquefaction process on land.

[0020] Compared with the prior art, the beneficial effects of the re-liquefaction system of the liquid hydrogen transport ship for recovering expansion work provided by the present invention include:

[0021] (1) The present invention uses hydrogen expansion cooling to provide cold energy for hydrogen, and then uses gaseous hydrogen to recover the expansion work generated during the expansion process to compress the gaseous hydrogen. While recovering the expansion work, it also reduces the usage and volume of the compressors in the system. After using this system, the compression energy consumption can be reduced by 5% - 10%.

[0022] (2) The present invention uses a gas bearing expander, and the bearing gas is hydrogen. Compared with oil bearings, the expansion work recovery process avoids the pollution of the hydrogen liquefaction system and does not need to bear the cost of oil removal.

[0023] (3) By setting a subcooler in the present invention, the flashing of liquid hydrogen is reduced, the evaporation loss of liquid hydrogen is small, and the safety hazard is small.

[0024] (4) Ideally, through the design of the expander parameters, after the first return flow stream and the second return flow stream leave the compression end of the expander, their pressures are the same as the expansion flow stream leaving the first heat exchanger. At this time, only one compressor unit is needed for pressurization. The number of compressors is reduced, the land use is saved by about 20%, and the cost of the system is saved.

[0025] (5) After the second return flow stream and the first return flow stream flow out of the second heat exchanger, as cold flow streams, they pass through the first heat exchanger and then flow through the compression end of the expander in sequence, making full use of the cold energy of these two flow streams and reducing cold energy waste.

[0026] (6) The present invention can be used for the re-liquefaction of liquid hydrogen transport ships and also for the hydrogen liquefaction process on land. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of an ideal design of a re-liquefaction system for a liquid hydrogen transport ship that recovers expansion work provided by the present invention;

[0028] Figure 2It is a schematic diagram under the general design of a re-liquefaction system for a liquid hydrogen carrier ship that recovers expansion work provided by the present invention.

[0029] Reference numerals:

[0030] 11 - First purifier; 12 - Ortho-para hydrogen converter; 13 - First heat exchanger; 14 - Second purifier;

[0031] 21 - Second heat exchanger; 22 - First J-T valve; 23 - Gas-liquid separator; 24 - Subcooler; 25 - Third J-T valve; 26 - Second J-T valve;

[0032] 31 - First expander; 32 - Second expander; 33 - Three-way valve; 34 - Pressure reducing valve; 41 - Compressor; 42 - Third heat exchanger. Detailed implementation manners

[0033] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0034] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0035] In addition, the terms "first" and "second" are only used for descriptive purposes, and do not refer to the limitation of time sequence, quantity, or importance. It cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features, but only to distinguish one technical feature in the technical solution of the present application from another technical feature. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0036] Unless clearly pointed out as mutually exclusive, each aspect or embodiment defined here can be combined with any other one or more aspects or one or more embodiments. In particular, any feature indicated as preferred or advantageous can be combined with any other feature indicated as preferred or advantageous.

[0037] The present invention provides a re-liquefaction system for a liquid hydrogen carrier ship that recovers expansion work, such as Figure 1 、Figure 2 As shown in Figure 2 , it includes a precooling unit, a hydrogen liquefaction unit, and a circulation unit. In some embodiments, the precooling unit includes a first heat exchanger 13, a first purifier 11, and an ortho-para hydrogen converter 12. The raw hydrogen stream is precooled by the first heat exchanger 13, and then sequentially passes through the first purifier 11 and the ortho-para hydrogen converter 12. The first purifier 11 is used to remove impurity gases in the raw hydrogen, and the ortho-para hydrogen converter 12 is used for ortho-para conversion. After the ortho-para hydrogen content is converted to the equilibrium state at the current temperature, it passes through the first heat exchanger 13 again and is cooled to the designed temperature range of the coolant.

[0038] In some embodiments, the hydrogen liquefaction unit includes a second heat exchanger 21, a first J-T valve 22, a gas-liquid separator 23, a subcooler 24, a second J-T valve 26, and a third J-T valve 25. After the raw hydrogen stream leaves the precooling unit, it sequentially passes through the second heat exchanger 21, the first J-T valve 22, and the gas-liquid separator 23. A para-hydrogen catalyst is provided in the raw hydrogen channel of the second heat exchanger 21, so that while the raw hydrogen is cooled to 30K ± 10K, continuous ortho-para conversion is also carried out until the para-hydrogen content is ≥ 95%. After passing through the first J-T valve 22, the raw hydrogen is divided into gas and liquid phases and separated in the gas-liquid separator 23. The gas phase returns to the second heat exchanger 21 as a cold stream. The liquid phase enters the subcooler 24 and is cooled to 18K ± 5K, and then is divided into a product stream and a second reflux stream. The product stream leads to a product collection container. After passing through the third J-T valve 25, the second reflux stream returns to the subcooler 24 and the second heat exchanger 21 as a cold stream in sequence and evaporates to form a second reflux stream.

[0039] In some embodiments, the circulation unit includes 1 - 3 compressor units 41 and at least one third heat exchanger 42, and several expanders are also provided, including a first expander 31 and a second expander 32. According to the actual needs of the hydrogen liquefaction process, the number of the first expander 31 and the second expander 32 is 0 - 4 each, and the total number of expanders is 2 - 5. Each expander includes a compression end. The compression end can utilize the expansion work generated when the expansion end expands the gas to compress the gas at the compression end. The expanders selected are gas-bearing expanders, and the bearing gas is hydrogen, which is provided by diverting a stream from the hydrogen compressed by the compressor unit or the compression end of the expander through a three-way valve 33. Before entering the bearing, the bearing gas is first decompressed to 0.6 - 0.8MPa by a pressure reducing valve 34 to make the pressure of the bearing gas meet the requirements. Using hydrogen as the bearing gas will not cause pollution to the hydrogen liquefaction system, and there is no need to consider matters such as oil removal, and dynamic pressure gas bearings or static pressure gas bearings can be selected.

[0040] The second reflux stream flows through the compression ends of all the second expanders 32 from the second heat exchanger 21, and the first reflux stream flows through the compression ends of all the first expanders 31 from the second heat exchanger 21. After being preliminarily compressed by using the expansion work, both of them lead to the compressor unit 41 and the third heat exchanger 42 and converge. The converged stream is denoted as the circulating hydrogen stream; further, after the second reflux stream and the first reflux stream flow out of the second heat exchanger 21, they first enter the first heat exchanger 13 for heating and then enter the corresponding expander compression ends. Further, the hydrogen liquefaction system of the present invention is also provided with a second purifier 14. The circulating hydrogen stream removes impurities through the second purifier 14. Molecular sieves or adsorbents such as activated carbon are provided in both the first purifier 11 and the second purifier 14 for adsorbing impurity gases.

[0041] The circulating hydrogen stream is precooled by the first heat exchanger 13 and then divided into an expansion stream and a makeup stream. The makeup stream sequentially passes through the second heat exchanger 21 and the second J-T valve 26 and then reaches the gas-liquid separator 23; then it is separated by the gas-liquid separator 23 to supplement the product liquid hydrogen so as to maintain the balance between the product liquid hydrogen and the raw material hydrogen quantity.

[0042] After the expansion stream is cooled and depressurized through the expansion ends of the second heat exchanger 21, the first expander 31 and the second expander 32, it flows as a cold stream to the second heat exchanger 21 and the first heat exchanger 13 in sequence and finally returns to the compressor unit, forming an expansion-compression cycle.

[0043] In an ideal case, as Figure 1 shown, through the design of the expander parameters, after the first reflux stream and the second reflux stream leave the compression ends of the expanders, their pressures are the same as those of the expansion stream leaving the first heat exchanger 13. At this time, only one compressor unit is needed for pressurization. The number of compressors is reduced and the cost of the system is saved. And in general cases, as Figure 2 shown, it can also be designed such that the first reflux stream or the second reflux stream has the same pressure as the expansion stream, and they can converge before entering the compressor unit, or the use of one compressor unit can be reduced.

[0044] The specific process steps can refer to the following embodiments. Embodiment

[0045] The hydrogen liquefaction system designed in this embodiment has a daily output of 10 tons. As Figure 1 shown, a re-liquefaction system for a liquid hydrogen carrier ship that recovers expansion work, and its hydrogen liquefaction process steps include:

[0046] S1: Pre-cool and purify the raw hydrogen gas through the first heat exchanger 13; use liquid nitrogen for pre-cooling, and the temperature of the hydrogen gas after pre-cooling is at 90K ± 10K; the pre-cooled gaseous hydrogen passes through the first purifier 11 to reduce the oxygen content in the gaseous hydrogen to below 0.1 ppm; the purified hydrogen gas passes through the ortho-para hydrogen converter 12 to convert part of the ortho-hydrogen in it into para-hydrogen, and the content of ortho-para hydrogen after conversion is roughly in the equilibrium state at 90K; due to the ortho-para conversion, the temperature of the gaseous hydrogen rises, so the converted gaseous hydrogen is pre-cooled again through the first heat exchanger 13 to make the gaseous hydrogen reach the lowest temperature of liquid nitrogen pre-cooling;

[0047] S2: The pre-cooled gaseous hydrogen enters the second heat exchanger 21, and an ortho-para hydrogen catalyst is installed in the raw hydrogen channel of the heat exchanger; while cooling the gaseous hydrogen, the second heat exchanger 21 also continuously performs ortho-para conversion on it until the temperature reaches 30K ± 10K; the cooled gaseous hydrogen passes through the first J-T valve 22 for throttling and pressure reduction to obtain gas-liquid two-phase hydrogen, and then reaches the gas-liquid separator 23. The separated gas phase forms the first return flow stream and returns to the second heat exchanger 21; the liquid hydrogen enters the sub-cooler 24 and is cooled to 18K ± 5K as the hot stream. The purpose is to reduce the flashing phenomenon of the generated liquid hydrogen, reduce evaporation loss and safety hazards. The sub-cooled liquid hydrogen is split into a product stream and a second return flow stream; most of the liquid hydrogen enters the liquid hydrogen storage tank through the product stream, and a small part of the liquid hydrogen enters the second return flow stream and is further depressurized through the third J-T valve 25. After depressurization, gas-liquid two-phase hydrogen is obtained as the cold stream and enters the sub-cooler 24. Among them, the liquid phase evaporates in the sub-cooler 24 and returns to the second heat exchanger 21 as the cold stream, and the evaporation process provides cold energy for the sub-cooler 24;

[0048] S3: After the gaseous hydrogen separated by the gas-liquid separator 23 fully utilizes its cold energy by passing through the second heat exchanger 21 and the first heat exchanger 13 in sequence, the compression end of the first expander 31 makes full use of the expansion work of its expansion end to compress it; after the second return flow stream fully utilizes its cold energy by passing through the second heat exchanger 21, it enters the compression end of the second expander 32 and makes full use of the expansion work of its expansion end to compress it. Then, the first and second return flow streams are mixed with the expansion stream and enter the compressor unit 41 for compression to 6.5MPa(A) ± 1.5MPa;

[0049] S4: The gaseous hydrogen compressed by the compressor unit 41 is first precooled through the first heat exchanger 13; the precooled gaseous hydrogen is divided into the expansion stream and the makeup stream. After the makeup stream is cooled to 30K ± 10K through the second heat exchanger 21, it is throttled and depressurized through the second J-T valve 26 to obtain gas-liquid two-phase hydrogen, and then separated through the gas-liquid separator 23 to supplement the product liquid hydrogen and maintain the balance between the product liquid hydrogen and the raw material hydrogen quantity; the expansion stream is continuously cooled to 30K ± 10K through the second heat exchanger 21, the second expander 32, the second heat exchanger 21, and the first expander 31 in sequence, and then returns to the second heat exchanger 21 to provide cooling capacity for all the hot streams; finally, after fully utilizing its cooling capacity through the first heat exchanger 13, it enters the compressor unit 41, and before entering the compressor unit 41, it converges with the first and second return streams to form the circulating hydrogen gas stream.

[0050] In this embodiment, an efficient molecular sieve is placed in the first purifier 11, which can effectively separate oxygen in hydrogen to make its content less than 0.1 ppm.

[0051] In this embodiment, the first heat exchanger 13 and the second heat exchanger 21 are efficient multi-stream heat exchangers, which can integrate all streams in one heat exchanger. Compared with the traditional process, the number of heat exchangers is reduced, the pipeline connection between heat exchangers is reduced, the energy loss caused by heat exchange between heat exchangers and external heat exchange is reduced, the volume of the cold box is reduced, the volume of evacuating the cold box is reduced, and the energy consumption of the vacuum pump is greatly reduced.

[0052] In this embodiment, the compressor unit 41 is an efficient oil-free fully balanced compressor. Compared with the traditional oil compressor, the use of the oil filter at the rear end can be reduced, the pressure loss through the oil filter is reduced, the use of the fully balanced compressor reduces the floor area of the compressor and also reduces the number of compressors used.

[0053] In this embodiment, the catalyst used in the catalytic refining is a metal catalyst, and the metal catalyst is one of iron, platinum, nickel, and palladium, or a magnetic catalyst can also be used.

[0054] In this embodiment, the second expander 32 and the first expander 31 are efficient gas-bearing expanders. A hydrodynamic gas bearing or a hydrostatic gas bearing can be used, and the bearing gas is hydrogen, which can reduce the requirements for the bearing seal of the expander; the bearing gas is provided by the compression end of the first expander 31. After a stream of hydrogen is separated from the compression end of the first expander 31 through a three-way valve 33, it is depressurized through a pressure reducing valve 34 and then introduced into the gas bearing. The second return stream and the first return stream make full use of their shaft work after passing through the compression ends of the second expander 32 and the first expander 31 respectively, reducing the compressor demand of the system and the compression energy consumption of the entire system.

[0055] In this embodiment, continuous sampling and analysis are performed on the gaseous hydrogen generated by the first purifier 11 and the ortho-para hydrogen converter 12, as well as the product liquid hydrogen, and a chromatograph is used as the analyzer.

[0056] In this embodiment, the third heat exchanger 42 cools the compressor unit 41 by water cooling or air cooling.

[0057] In this embodiment, the hydrogen liquefaction system includes a control device. Temperature sensors, pressure sensors, and flow sensors are respectively provided in the first heat exchanger 13, the second heat exchanger 21, and the ortho-para hydrogen converter 12, and are connected to the control device that controls the hydrogen liquefaction process flow.

[0058] The present invention uses hydrogen expansion cooling to provide cold energy for hydrogen, and then uses gaseous hydrogen to recover the expansion work generated during the expansion process to compress the gaseous hydrogen. While recovering the expansion work, it also reduces the usage and volume of the compressors in the system. After using this system, the compression energy consumption can be reduced by 5% - 10%.

[0059] The present invention uses a gas bearing expander with hydrogen as the bearing gas. Compared with an oil bearing, the expansion work recovery process avoids contamination of the hydrogen liquefaction system and does not require the cost of oil removal.

[0060] The present invention reduces the flashing of liquid hydrogen by setting a subcooler, resulting in small evaporation loss of liquid hydrogen and small potential safety hazards.

[0061] Through the design of the expander parameters, after the first return flow stream and the second return flow stream leave the compression end of the expander, their pressures are the same as the expansion flow stream leaving the first heat exchanger. At this time, only one compressor unit is needed for pressurization. The number of compressors is reduced, saving about 20% of the land area and saving the cost of the system.

[0062] After the second return flow stream and the first return flow stream flow out of the second heat exchanger, as cold flow streams, they pass through the first heat exchanger and then flow through the compression end of the expander in sequence, making full use of the cold energy of these two flow streams and reducing cold energy waste.

[0063] The present invention can be used for the reliquefaction of liquid hydrogen transport ships and also for the hydrogen liquefaction process on land.

[0064] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and substitutions to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims

1. A re-liquefaction system for a liquid hydrogen carrier ship that recovers expansion work, characterized in that, Comprising: a precooling unit, a hydrogen liquefaction unit, and a circulation unit; The precooling unit comprises a first heat exchanger for precooling a feed hydrogen stream; The hydrogen liquefaction unit comprises a second heat exchanger, a gas-liquid separator, and a subcooler; after the feed hydrogen stream leaves the precooling unit and forms a gas-liquid two-phase through the second heat exchanger, it reaches the gas-liquid separator, where the gas phase is denoted as the first reflux stream and returns to the second heat exchanger as a cold stream; while the liquid phase enters the subcooler and is cooled to 18K ± 5K and then split into a product stream and a second reflux stream; the product stream leads to a product collection container; after the second reflux stream undergoes throttling and pressure reduction, it returns to the subcooler and the second heat exchanger as a cold stream in sequence; The circulation unit comprises at least one compressor unit and a number of expanders; each expander comprises a compression end that uses the expansion work of the expander to pressurize the gas; the expander is a gas-bearing expander; the bearing gas is hydrogen, which is provided by diverting a stream of hydrogen from the compression end of the compressor unit or the expander; before entering the bearing, the bearing gas is first reduced in pressure to 0.6 - 0.8MPa through a pressure reducing valve; the expander comprises a first expander and a second expander, and the number of the first and second expanders is 0 - 4; after the first reflux stream flows through the compression end of the first expander from the second heat exchanger, and after the second reflux stream flows through the compression end of the second expander from the second heat exchanger, both lead to the compressor unit and merge, and the merged stream is denoted as the circulating hydrogen stream; The circulating hydrogen stream is precooled by the first heat exchanger and then split into an expansion stream and a make-up stream, and the make-up stream reaches the gas-liquid separator after passing through the second heat exchanger; After the expansion stream is cooled and depressurized through the second heat exchanger and the expansion end of the expander, it also flows to the second heat exchanger and the first heat exchanger as a cold stream in sequence, and finally returns to the compressor unit and is incorporated into the circulating hydrogen stream; The hydrogen liquefaction unit is also provided with a first J-T valve, a second J-T valve, and a third J-T valve for throttling and pressure reduction; after the feed hydrogen stream passes through the second heat exchanger, it also passes through the first J-T valve for cooling and pressure reduction to form a gas-liquid two-phase; the make-up stream, after passing through the second heat exchanger, also passes through the second J-T valve for cooling and pressure reduction to form a gas-liquid two-phase; after the second reflux stream undergoes throttling and pressure reduction through the third J-T valve, it returns to the subcooler and the second heat exchanger as a cold stream in sequence; A normal-hydrogen to para-hydrogen catalyst is provided in the feed hydrogen channel of the second heat exchanger for continuous normal-hydrogen to para-hydrogen conversion of the feed hydrogen; The system comprises a control device, and temperature sensors, pressure sensors, and flow sensors are respectively provided in the first heat exchanger, the second heat exchanger, and the normal-hydrogen to para-hydrogen converter and are connected to the control device.

2. The system according to claim 1, wherein The normal-hydrogen to para-hydrogen catalyst is a metal catalyst or a magnetic catalyst, and the metal catalyst is one of iron, platinum, nickel, and palladium.

3. Use of the system according to claim 1 or 2, characterized in that, For the hydrogen liquefaction process on land.

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